The present invention relates to monitoring interventional medical devices (IMDs). More particularly, the present invention relates to an ultrasonic system of monitoring the proximity and alignment of the IMD relative to a tissue surface.
Interventional medical devices (IMDs), such as catheters and surgical lasers are used for many medical procedures. Laparoscopy, the insertion of a fiber optic instrument into the abdomen, is just one relatively common type of IMD procedure. Minimally invasive surgery (MIS) is a term that, as used in this disclosure, encompasses a broader range of such procedures, and in which an IMD is introduced into the patient through a relatively small incision. A major problem inherent with the use of IMDs in MIS procedures is detecting the current location and orientation of the IMD, and remotely guiding it within a patient. It would be desirable to have an apparatus or method that assisted in precisely determining the location and orientation of a wide range of IMDs. It would be particularly desirable to have an apparatus or method for determining when the distal end of the IMD is in contact with and perpendicular to a tissue surface.
U.S. Pat. No. 5,109,859 issued to Jenkins on May 5, 1992 (the ""859 patent), discloses an ultrasound guided laser for use in angioplasty. The ""859 patent is specifically directed at a method of imaging the lateral walls of arteries for laser ablation procedures and can not easily be adapted to function with a wide range of IMDs.
U.S. Pat. No. 5,313,950 issued to Ishikawa, et al. on May 24, 1994 (the ""950 patent), discloses an ultrasonic probe for providing images in hollow objects such as blood vessels. The ""950 patent, like the ""859 patent, creates images at 90xc2x0 to the longitudinal axis of the IMD. This lateral imaging provides little data for determining IMD alignment and indicating when the distal end of the IMD is in contact with a tissue surface.
U.S. Pat. No. 5,377,682 issued to Ueno, et al. on Jan. 3, 1995 (the ""682 patent) also teaches an ultrasonic probe for imaging perpendicular to the longitudinal axis. Again, there is no description which assists in determining alignment of the probe and indicating when the distal end of the IMD is in contact with a tissue surface.
U.S. Pat. No. 5,893,848 issued to Negus, et al. on Apr. 13, 1999 (the ""848 patent), teaches a gauging system for monitoring the depth of an IMD as it penetrates into heart tissue. However, the ""848 patent does not provide data on the proximity of the IMD to the tissue surface prior to penetrating the surface, nor does it indicate the angle of the IMD relative to the tissue surface.
U.S. Pat. No. 6,024,703 issued to Zanelli, et al. on Feb. 15, 2000 (the ""703 patent), measures the distance between the distal end of the IMD and the tissue surface both prior to contacting the surface and after penetrating the surface. This invention is primarily directed at measuring the distance between a laser IMD that has penetrated the tissue surface and the rear surface of that tissue. It is not as well suited for providing positional data prior to the laser penetrating the tissue, or for indicating when contact has been made between the IMD and the front surface of the tissue. A weakness of the device taught in the ""703 patent is the inability to achieve high measurement accuracy when the IMD is very close to, or in contact with, the tissue surface. It would be desirable to accurately determine the IMD proximity to the tissue surface when it is close to the tissue surface, as well as accurately indicating contact with the tissue surface.
A method and apparatus for remotely monitoring the location of an interventional medical device (IMD) using ultrasonic signals. Both the proximity and alignment of the IMD are calculated from ultrasound signals reflected off the tissue surface. The inclusion of an offset between the distal end of the IMD and the ultrasound transducer enables accurate position and alignment monitoring of when the IMD is in contact with, or very close to, the tissue surface. The timing of the reflected signal is used to measure proximity or contact. A comparison of the strength between multiple reflected signals is used to measure the alignment of the IMD in 3D space or perpendicularity to a given surface. The present invention may be used as a location indicator with a wide variety of IMDs, and in a wide variety of medical procedures.